Who Is Drinking Nitrate in Their Well Water?

Groundwater contamination with nitrate is a pervasive and serious problem. It is a health threat because of population expansion into rural areas, and an increasing population which relies heavily on private water systems. In Oregon, groundwater use is expected to expand in proportion to the rate of population growth (1). Little has been known about the quality of private well water supplies in Oregon because, until recently, these systems were not routinely monitored by their users or any governmental agency. Legislation in 1991 required testing of well water for nitrate and total coliform bacteria, but only when properties were sold or exchanged (2).

Approximately twenty years ago the World Health Organization recommended a maximum contaminant level (MCL) of 10 ppm nitrate nitrogen (nN) in drinking water (3). The United States Environmental Protection Agency (USEPA) and a majority of state agencies which oversee drinking water programs adopted this level as an indicator of potential health risk posed by drinking-water exposure to nitrate (4). The most common health concern is methemoglobinemia, or "blue-baby syndrome," a potentially fatal condition which inhibits the ability of red blood cells to bind and transport oxygen (5). Nitrate and nitrite have also been linked to such conditions as cancer, mutagenic and teratogenic effects (5,6), birth defects (6), behavioral and developmental abnormalities (7), and cardiovascular disease (8). A more detailed review of the health effects associated with nitrate exposure is found in a recent report published by the Oregon Water Resources Research Institute (9).

Groundwater Contamination in the LUB

It has been known for several years that much of the groundwater in the Lower Umatilla Basin (LUB) of Umatilla and Morrow Counties of northeastern Oregon is contaminated with nitrate. A 1995 project report indicates that of 850 LUB groundwater samples for nitrate taken between 1990 and 1993, approximately 30% had nitrate levels over 10 ppm, 44% had nitrate levels between 2 ppm and 10 ppm, and the remaining 26% of the samples had nitrate levels under 2 ppm (10). This rural region also has a high concentration of private domestic water wells.

Land use is a major reason for current levels of nitrate contamination in the LUB. First, the area has a history of intensive farming practices using fertilizers and field irrigation methods. The nitrogen in nitrogen-containing fertilizers applied to crops, and not fully utilized by plants and soil organisms, may leach to groundwater. Second, a food processing industry operates within the same region resulting in an abundance of readily-available, nitrogen-rich plant residues and liquid wastes. If these wastes are land-applied to supplement chemical fertilizers, there is a tendency to over-fertilize and increase the potential for leaching of nitrate to groundwater. Third, septic systems are in common use in the LUB. Nitrate may leach to groundwater from leaking septic tanks, improperly constructed leach fields, failed systems, and even from properly operating septic systems.

Geology and precipitation also are important factors in nitrate contamination to groundwater. The LUB is an arid, 780-square-kilometer area, receiving an annual precipitation of less than 25 cm. The soils are predominantly sandy and the aquifers are shallow and unconfined. Irrigation water applied to crops under this set of conditions, if in surplus of plant requirements, can leach nitrate to groundwater. These relatively unprotected aquifers are also the most vulnerable to pollution and the buildup of contaminants over time.

Although high well water nitrate levels have been documented in some areas of the state, no studies have been conducted which evaluate the extent of population exposure to this nitrate source. The purpose of this study was, therefore, to document demographic characteristics of domestic well users in the LUB, and to evaluate whether or not this population is potentially at risk from drinking well water containing nitrate. …

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